1. Field of the Invention
The present invention relates to an optical recording medium-manufacturing apparatus that manufactures an optical recording medium by punching a central hole through a disk-shaped substrate.
2. Description of the Related Art
In general, when an optical recording medium (optical disk), such as a Blu-ray Disc (BD), is manufactured, a thin film, such as a light-reflecting layer, is formed on a disk-shaped substrate having grooves and lands formed in a surface thereof by injection molding, and then a resin layer (light transmission layer) having a thickness of approximately 100 μm is formed on the thin film by the spin-coating method such that the resin layer covers the thin film. In the Blu-ray Disc, a construction is employed in which a laser beam emitted e.g. from a playback apparatus transmits through the resin layer. Consequently, if the optical recording media thus manufactured has variation in the film thickness of the resin layer thereof, it is difficult to normally reproduce recorded data. Therefore, in the formation of a resin layer, it is necessary to spin-coat the entire surface of a substrate with a resin material for forming a resin layer, to a uniform thickness. In this case, to form a resin layer having a uniform thickness on a substrate by the spin-coating method, it is preferable to drop a resin material onto the center of a substrate being rotated. To this end, there has been proposed a method of manufacturing an optical recording medium by dropping a resin material onto the center of a substrate before forming a central hole for clamping, which is required in reproduction of recorded data e.g. by a playback apparatus, to thereby form a resin layer having a uniform thickness, inserting a hollow-cylindrical punching blade section from the reverse side of the substrate, and then punching the central hole such that the central hole extends through the substrate and the resin layer.
However, this optical recording medium-manufacturing method suffers from the problem that due to vertical motions of the punching blade section during punching of the central hole, the resin layer or the substrate through the central hole 1 is to be formed is not clearly punched out, but the rim of the central hole suffers from peeling or burring of the resin layer. To form a uniform resin layer while overcoming this problem, the present assignee has proposed in Japanese Patent Application No. 2002-276491, an optical recording medium-manufacturing apparatus (hereinafter also referred to as the “manufacturing apparatus”) which manufactures an optical recording medium by forming a cut in a resin layer before pushing a punching blade section into the resin layer, and then pushing the punching blade section from the reverse side of a substrate while causing ultrasonic vibration of the punching blade section, to thereby form a central hole by punching.
In this manufacturing apparatus, first, a cut is formed in the resin layer formed on one or front surface of the substrate. More specifically, in a state of a retaining jig being in abutment with the other or reverse surface of the substrate, another retaining jig formed with a cut-forming blade section having a height slightly larger than the thickness of the resin layer is moved downward toward the resin layer to thereby push the cut-forming blade section into the resin layer. Thus, the cut is formed in the resin layer. Then, a central hole is formed by punching. More specifically, the punching blade section is caused to move upward from the reverse side of the substrate while causing ultrasonic vibration of the punching blade section by ultrasonic waves generated by a ultrasonic generator. In this case, a portion of the substrate in contact with the punching blade section is softened due to heat generated by ultrasonic vibration of the punching blade section, so that the punching blade section is smoothly pushed into the substrate. As a result, the wear of the cutting edge of the punching blade section is reduced.
Next, when the punching blade section is further moved upward and the cutting edge of the punching blade section reaches the front surface of the substrate, the punching of the substrate is completed to form the central hole. This completes the optical recording medium. In this case, since the cut has been formed in the resin layer by the cut-forming blade section, when the cutting edge of the punching blade section reaches the one or front surface of the substrate, a portion of the substrate inward of the cut is clearly cut off along the cut by the force of moving the punching blade section upward. As a result, it is possible to prevent the rim of the central hole from suffering from peeling or burring of the resin layer.
However, from the study of the proposed manufacturing apparatus, the present inventors found out the following points for improvement: In the proposed manufacturing apparatus, a cut is formed by pushing the cut-forming blade section of the retaining jig into the resin layer. The resin layer has a sufficient hardness for protection of a light reflection layer or a recording layer, and at the same time, a relative large thickness of approximately 100 μm, so that the cutting edge of the cut-forming blade section sometimes wears out in a relatively short time period. If the cut-forming blade section having the worn cutting edge is used, it is difficult to form a cut having a sufficient depth for ensuring prevention of peeling or burring of the resin layer. Therefore, it is necessary to replace a cut-forming blade section frequently (e.g. every 5000 to 10000 times of cutting operation). Therefore, this manufacturing apparatus can cause an increase in manufacturing costs owing to replacement of lots of cut-forming blade sections and lowered manufacturing efficiency caused by frequent replacing operations. This inconvenience is desired to be eliminated. To this end, it can be contemplated to provide separately from the above-mentioned ultrasonic generator, an additional ultrasonic generator for causing ultrasonic vibration of the cut-forming blade section, and cause the cut-forming blade section to be pushed into the resin layer while causing the additional ultrasonic generator to cause the ultrasonic vibration of the cut-forming blade section. This method, however, requires provision of two ultrasonic generators which are very expensive, causing an increase in the component costs of the manufacturing apparatus. This makes the method difficult to employ.